Minimal A4 Type-II Seesaw Realization of Testable Neutrino Mass Sum Rules

TL;DR

This paper introduces a minimal A4 flavor model with a type-II seesaw mechanism that predicts the neutrino mass spectrum, mixing parameters, and neutrinoless double beta decay rate, all testable with current experiments.

Contribution

It presents a novel A4-based flavor model with a type-II seesaw that fully determines neutrino masses and mixing, linking them to observable lepton-number-violating processes.

Findings

Predicts inverted neutrino mass ordering.

Restricts Majorana phases and predicts maximal neutrinoless double beta decay rate.

Suppresses muon flavor violation, allowing specific tau decay channels.

Abstract

We propose a flavour model based on an $A_4$ symmetry combined with a type-II seesaw mechanism for neutrino mass generation. The resulting neutrino mass matrix obeys a sum rule that, together with the measured mass-squared differences, fully determines the absolute neutrino mass spectrum. The constrained flavour structure yields correlated predictions for lepton mixing parameters, leads to inverted ordering after imposing mixing constraints, restricts the Majorana phases and implies a neutrinoless double beta decay rate close to its maximal value for inverted ordering. In the charged lepton sector an approximate triality symmetry arises in the seesaw limit, suppressing muon flavour-violating processes and allowing only specific $\tau$ decay channels. The model provides a tightly constrained and experimentally testable framework linking neutrino masses, lepton mixing and lepton-number-violating observables.